The development of wireless communication systems has increased the demand for monolithically integrated, low-cost and low-phase-noise voltage controlled oscillators (VCO:s). One known type of VCO is the so-called Hartley VCO. Such VCO:s are known to enable good phase noise performance at high frequencies, e.g. >15 GHz [1]. A Hartley VCO uses two inductors [2], which differs from other popular VCO topologies, e.g. Colpitts VCO and cross-coupled VCO. However, the so-called Armstrong VCO [3], [4] also uses two inductors.
In radio frequency (RF) or microwave monolithic (MM) integrated circuits (IC), an inductor is often much larger than a transistor, or other components. It thus consumes most of the chip area. With the scaling to ever-smaller dimensions of transistors, the manufacturing costs per square millimeter chip area increases significantly. Therefore, if chip size is at a premium, an instinctive choice is using as few inductors as possible. Consequently, the Hartley VCO by tradition has been deemed unsuitable for RFIC or MMIC applications, in terms of chip area costs caused by the use of two inductors.
There is therefore a need for a monolithically integrated Hartley VCO with reduced chip area requirements.